For years, the information technology department at Western Union had a policy of issuing and supporting only BlackBerry devices for its mobile workers. The rule was a strict one, because the BlackBerry’s security features were the only ones that met the company’s standards. Then, in September, a new CEO, Hikmet Ersek, took command of the 6,000-employee enterprise and demanded that he be allowed to use his iPhone for work. The demand coincided with a broader corporate strategy aimed at moving faster to offer Western Union’s famous money-transfer service on all mobile devices.

Reluctantly, the chief information officer, John Dick, was forced to comply. “We need to give our employees more freedom,” Dick said at an industry conference last month. But he also acknowledged that it would take several months for the company to fully authorize and support the iPhone and Android devices.

What is your preferred smart-phone platform?A survey of nearly 200 enterprise IT decision makers shows widening support for multiple operating systems. More than half prefer the BlackBerry today, but three-quarters expect to prefer a different platform two years from now.

The increased diversity, capability, and popularity of smart phones is leading to a fundamental change in the way mobile technology is being handled in large businesses. Once upon a time, you started a job and IT would provide you with a corporate-sanctioned computer and, for millions of employees, a BlackBerry—a device that became synonymous with mobile e-mail. Most important, the BlackBerry gave corporate IT departments control over what employees could and couldn’t do with their devices.

The landscape has shifted dramatically over the past year. The explosion of new devices featuring high-resolution screens, engaging user interfaces, and access to entire app stores has ignited a revolution at the workplace. More and more companies have had to respond to the popular preference for BYOD (“bring your own device”) policies. Sometimes the change comes from the bottom up, but sometimes, as with Western Union, it comes from the top down. Either way, it often leads to a clash between freedom and security, a conflict that’s especially tricky now that mobile phones are used interchangeably for both personal and professional purposes.

At some companies, the IT department won’t budge. ING Investment Management Services issued BlackBerry phones to more than 1,000 employees and prohibited the use of anything else for work. As a global financial firm that manages billions of its clients’ dollars, it is naturally concerned about data confidentiality, and it has spent years testing and implementing BlackBerry security functions. Its BlackBerrys run an app that monitors text messaging, in order to enforce a rule that employees cannot send texts unless they are traveling abroad. Employees’ use of instant messaging is strictly audited.

But with the allure of rival mobile devices, “there’s constant conflict around here,” says Michele Thurston, ING’s BlackBerry administrator. “Sales and marketing want the iPhone because they want to do streaming video, which the BlackBerry can’t do.” She notes that another financial-services company recently started supporting Droid devices, whose main screen makes it easy to access applications such as Skype. “I’d have to have a whole team just to manage all that,” Thurston laments.

Apple’s iPhone, Google’s Android, and Nokia’s Symbian platforms have all made significant progress toward meeting such key enterprise requirements as support for the data synchronization technology Exchange ActiveSync, which offers many security features for e-mail. They’ve also introduced remote data wiping and remote locking in case the phone gets lost. And IT departments can distribute and manage applications on the devices remotely.